Homing system



11w. CHEW HOHING SYSTEM i hllvali Filed Dec. 10, 1945 3 Sheets-Sheet 1 PRE-AM gvwowkw THORNTON W. C" EW M y 1947. T. w. CHEW HOMING SYSTEM Filed Dec. 10, 1945 3 Sheets-Sheet 2 3mm CHEW THORNTON W.

T. W. CHEW 50mm SYSTEM Filed D60. 10, 1945 3 Sheets-Sheet 3 3mm W. CHEW monm' Patented May 27, 1 947 V UNITED STATES PATENT FFICE HOMING SYSTEM Thornton W. Chew, United States Navy Application December 10, 1945, Serial No. 634,185

(01. 250-4115) (Granted under the act of March 3, 1883, as

16 Claims.

My invention relates to homing systems for automatic guidanceoi movable objects, such as bombs or aircraft, toward movable or stationary objectives such as targets or landing areas.

In general, vertical and horizontal surfaces for steerin of the object are actuated in response to deviation of images of the target from vertical and horizontal reference lines each between a pair of adjoining photo-cells responsive to radiation from the target.

the photo-cells having the horizontal reference line is substantially greater than the fleldof view of the optical system associated with the photocells having the vertical reference line, thus to take into consideration that the quadhedral angle of approach to the target is of greater magnitude in horizontal direction than it is in vertical direction.

In accordance with another aspect of my invention, the amplifier system, necessarily interposed between thephoto-cells and the actuating mechanisms for the steering apparata' is simplified by use of a common amplifier channel for both pairs of photocells and by providing an output filter system therefor which segregates signals from the different pairs of cells in accordanc with their corresponding carrier frequencies as produced by periodic interruption, at different frequencies, of the radiationto the different pairs of cells. In accordance with another aspect of my invention, to afford correction for deviations from proper course in minimum time without excessive hunting, it is provided that the signal output of each pair of photo-cells shall increase at greater and greater rate for successive equal increases in deviation from the homing course.

My invention further resides in the methods,

systems and components having features hereamended April 30, 1928; 370 0. G. 757) 2 Fig. --3 comprises a side view of the shutter shown in Fig. 2 and a schematic diagram of the gliectil'ical control system shown in block form in g. Fig. 4 is an explanatory figure referred to in discussionof photo-cell characteristics.

Figs. 5, 6 and 7 illustrate various forms' of photo-cells particularly suited for use in the control system shown in Figs. 1 and 3.

Fig, 8 illustrates an optical filter for use with photo-cells included in the control system shown in Figs. 1 and 3.

Referring to Fig. 1, the missile l which may be a bomb or a self-propelled craft is provided with a control surface such as rudder 2 movable to steer it toth right or left and control surfaces such as vane 3 to steer it up o down. These control surfaces are automatically-actuated as hereinafter described to correct for deviations from proper course.

The control system for rudder 2 includes a pair of photo-cells R, L whose net output is zero when a radiation image of the target is equally distributed between the sensitive areas of the two cells, that is equally distributed on opposite sides of thexvertical reference line V-V. Ifthe target image is not so centered, the output of oneor the other of cells R, L predominates and the rudder 2' is actuated by its servo-control mechanism 4 to turn the missile i in proper direction to attain a centered target image. j N

. Similarly, when the target image is not equally distributed above and below the horizontal reference line H-H of a second pair of photo-cells U,

D the servo-control mechanism 5 tilts the vane 3 in proper sense to re-center the target image.

Because the probable angle of approach of the target is greater horizontally than vertically, it is desirable that the angle. of viewof the radiationsensitive system comprising the photo-cells R, L, U and Dbewider in a horizontal plane than in a. vertical plane. This objective is attained by use of a wide-angle cylindrical lens 6 for focusin the target image on photo-cells R,'L and a narrower-angle cylindrical lens I for focusing the target image on photo-cells U, D. The axes of the lenses are mutually perpendicular in a plane transverse to their optical axes which are parallel, the high ratio of distance to the target to the distance between the optical axes of the q lenses making parallax of negligible effect on ac- .curacy of .the control. The lenses may be of any Fig. 2 is a front'view on enlarged scale of-a romaterial suitably transparent to the radiation,

1 visible orinvisible to the eye, utilized.

Useof the cylindrical type of lens is crad- =signal current =total current F=total incident radiation AF=radiation from target However, the relationship between signal current (AI), area of the target image (Ai) and area of the photo-cell element (Ae) is expressed,

when the radiation flux-density of the image is constant. by

From these two formulae, it appears that maximum signal current from a given quantum of radiation in the target image is realized when that image is distributed evenly over the photosensitive area.

For purposes of this invention such even distribution cannot be fully employed because for control purposes sharp definition is required in the h. dimension (measured in direction normal to the reference line H-H or V-Y) Therefore, a cylindrical lens is used to enlarge the target in its w dimension (parallel to the reference line V-V or H-H); that is, the target image is distorted to have a sharply defined height but approximating in length the width" of the photoconductive area.

Accordingly the target image as seen by the conjugate cells R, L is distorted by vertical expansion and as seen by conjugate cells U, D, is distorted by horizontal expansion.

In other homing systems which locate the po-v sition of the target with respect to four quadrants of the field of view, four amplifier channels have been provided to afford up-down and right-left control of the missile. As hereinafter more specifically explained, the number of required amplifier channels is reduced by generating carrier frequencies modulated in accordance with up-down and right-left signals respectively, by passing the different carrier frequencies through a common alternating current amplifier, of one or more stages, having a response bandwidth sufiicient to include the different carrier frequencies, and by thereafter separating the different carriers, as by filter circuits, for application to the respective servo-mechanisms.

The arrangement for generating the carrier currents may comprise a chopper disk 8 whose inner section, alternately opaque and transparent, interrupts the path of radiation to the other pair of cells.

Rotation of disk 8 may conveniently be effected by propeller 9 and gears l0, ll attached respectively to the propeller andthe disk.

In the interest of compact design and reliable electrical operation, the diameter of disk 8 should be as small as possible consistent with circumference sufliciently large to accommodate an adequate number of the higher-frequency chopper segments. If the ratio of chopper segments in the outer and inner disk sections is too low, the

difference between the carrier frequencies is too slight for separation of the different frequencies without recourse to elaborate filters.

To obtain maximum carrier current, each pair of cells must alternately be completely exposed to and completely shut off from the radiation. Consequently, the dimensions of the cellsv chosen determine the optimum minimum arc of the chopper segments. When the image-receiving surface of a pair of cells is round or square, the relation of the maximum dimension to the minimum dimension of each cell is about two to one.

The reference line V--V of cells R, L is in alignment with the vertical radius of the chopper wheel, and the reference line H-H of cells U, D is parallel to the horizontal diameter of the chopper wheel. Accordingly, the cells R, L continuously scan a target image along a vertical line of resistance and the other pair of cells continuously scans a similar image along a horizontal line of resistance, thus continuously and simultaneously to provide signals concurrently amplified and concurrently utilized for simultaneous right-left and up-down correction of the course of the missile.

The common terminal of cells R, L is connected to the cathodes of amplifier tubes l2, l3 in a current path including battery l4 or equivalent source of current. Similarly the common terminal of cells U, D is connected to these same cathodes in a current path including battery l5 or equivalent.

The control electrode of tube I2 is connected to the other terminals of cells R and D and the control electrode of tube I3 is connected to the other terminal of cells L and U. The filters Fl, Fl in the output system of tubes l2 and I3 accept or pass the higher carrier frequency conveying the right-left signals and reject or discriminate against the lower carrier frequency. The signals passed by filter Fl control the position of rudder 2 through the servo-system 4 including tubes l6, l1 and the differential magnet system comprising coils l8, l9 disposed respectively in the anode circuits of tubes l6, l1 jointly to determine the position of their common armature 20 suitably connected to the rudder. The filters F2 pass the lower signal frequency, to the substantial exclusion of the higher signal frequency, for control of the position of vane 3 through the servosystem comprising tubes 2 l, 22, coils 23, 24 in the respective anode circuits thereof, and the common armature 25.

To ensure rapid correction of deviations from proper course without excessive overshooting or hunting, it is provided that the signal output shall increase at greater and greater rate for successive equal increases in magnitude of the angle of deviation from the homing course. As hereinafter more specifically appears, Figs. 5 to 8,

this may be attained by varying the lengthor The change in carrier current AI resulting from photo-conductive reaction to a target image is Substituting Equation 1 in Equation 3 v ARw Substituting Equation 2 in Equation 4 AR K w (5) It is thus seen that all other factors remaining constant, the change in carrier current is directly proportional to the width of and inversely proportional to the height of the photesensi- I tive area.

In the modified form of photoscell shown in Fig. 5, a plurality of electrodes are connected to each terminal of the cell, the spacing between adjacent electrodes, of opposite polarity decreasing with increasing distance from the reference line H--H 0r V-V. The width of the photosensitive film is, in this modification, constant for all sections of the cell but the height of the film. progressively decreases for the more and more remote sections.

When a given target image moves for example from section Rn to the next section Rn+1. the factor of change "a produced in these elements may be expressed as (6) l mmin s. Expressed in terms of elemental areas, Equation 6. by substitution of Equation 1, becomes In the modification shown in Fig. 7, both the width and height of the successive cell elements vary as a function of the distance from the reftargetimage from: the reference line H- -H or V V increases.

Itshallbe understood my invention is-notlim ited to specific arrangements herein disclosed but is coextensivein scope with the appended claims.

photo-cells having a wider angle of view in the horizontal plane than in the vertical plane.

2. A system for steering an object in horizontal and vertical directions toward a target com-. prising pairs of photo-cells disposed to generate steering signals in accordance with deviations of radiation images of the target from horizontal and vertical reference lines, and an optical system for impressing said images on said cells comprising cylindrical lenses disposed with their axes respectively parallel to said reference lines.

3. A system for steering an object toward a target comprising a pair of photo-cells for generating a signal foreffecting right-left steering control, a cylindrical lens for impressing an image of the target on said first pair of cells, and a second cylindrical lens having a substantially greater field of view than the first-named lens for impressing an image of the target on said second pair of cells.

4. A system for generating signals in accordance with deviations of a radiation image from angularly displaced reference lines com-prising two pairs of photocells, the cells of each pair being disposed on opposite sides of one of said reference lines, and an optical system comprising cylindrical lenses each for impressing a radiation image on one of said pairs of cells.

5. A system for generating signals in accordance with deviations of a radiation image from a reference'line comprising a pair of photo-cells disposed respectively on opposite sides of said line, and a cylindrical lens having its axes parallel to said line for impressing said image on said cells.

I 6. A system for steering an object toward a target comprising photo-cells for generation of signals effecting up-down and right-left steering control, a common amplifier upon which said signals are impressed, means in advance of said erence line H--H or V-V. In such case the factor of change "a may be expressed as amplifier channel for varying the up-down and right-left signals at different frequencies, and filter means on the output side of said amplifier for segregating said difierent frequencies for transmission in different paths.

'7. A system for steering an object toward a target comprising pairs of photo-cells for'generation of signals effecting up-down and rightleft steering control, a common amplifier upon which said signals are impressed, means for interrupting at different rates the paths of radiation from said target to said pairs of cells to generate diiferent carrier frequencies for said signals, and filter means on the output side of said amplifier for segregating said different frequencies.

8. A system for steering an object toward a target comprising pairs of photo-cells for generation of signals efiecting up-down and rightleft steering control, a common amplifier upon which said signals are impressed, rotating shutter means for interrupting at diflerent rates the paths of radiation from said target to said pairs of cells to generate different carrier frequencies ing concentric rows of angularly spaced segments,

a pair of photo-cells disposed on opposite sides of a vertical reference line normal to the axis of rotation of said shutter and receiving radiation in a path interrupted by one of said rows of segments, and a second pair of photo-cells disposed on opposite sides of a horizontal reference line and receiving radiation in a path interrupted by another row of said segments.

10. In a control system, a pair of photo-cells disposed on opposite sides of a reference line for generating signals varying in accordance with deviation of a radiation image from said reference line, each of said cells having electrodes parallel to and at diiferent distances from said reference line and the ratio of height to width of successive cell areas defined by said electrodes varying as a function of their distance from said reference line.

11. In a control system, a pair of photo-cells disposed on opposite sides of a reference line for generation of signals varying in accordance with deviationof a radiation image from said reference line, each of said cells having electrodes parallel to said reference line with the spacing between adjacent electrodes decreasing with increase of distance from saidreference line.

12. In a control system, a pair of photo-cells disposed on opposite sides of a reference line for generation of signals varying in accordance with deviation of a radiation image from said reference line, each of said cells having electrodes parallei'to said reference line and bounding areas of photo-conductive material whose width varies as a function of distance from the reference line.

13. In a control system, a pair of photo-cells disposed on opposite sides of a reference line for generation of signals varying in accordance with deviation of a radiation image from said reference line, each of said cells having electrodes parallel to said reference line with the spacing between successive pairs of electrodes decreasing with increase of distance from said reference line and with the width of photo-conductive material between successive pairs of adjacent electrodes varying as a function of distance from said reference line.

'14. In a control system, photo-cells disposed on opposite sides of a reference line for generation of signals varying in accordance with deviation of a radiation image from said reference line, and an optical filter in front of said cells of opacity decreasing with increase of distance from said reference line,

15. A system for correcting the course of an object moving toward a target in accordance with deviation of. images of the target from vertical and horizontal reference lines comprising two crease of deviation of the image from the asso- I ciated reference line.

16. A system for correcting the course of an object moving toward a, target in accordance with deviation of images of the target from horizontal and vertical reference lines comprising two pairs of photo-cells, the cells of each pair being disposed on opposite sides of one of said reference lines, a pair of cylindrical lenses having their axes respectively parallel to said reference lines to impress radiation images of the target on said pairs of cells, movable shutter means for interrupting the paths of radiation to said cells to vary their outputs at different carrier frequencies, means for increasing the output of each pair of cells disproportionately to increase of deviation of the target image from the associated reference line, a common amplifier upon which the outputs of said cells are impressed, and filter means on the output side of said amplifier for segregating the different carrier frequencies for transmission .in difierent paths.

THORNTON W. CHEW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,388,932 Centervall Aug. 30, 1921 1,747,664 Droitcour Feb. 18, 1930 1,016,240 Alexieff Jan. 30, 1912 2,403,387 McLennan July 2, 1946 2,164,916 Hammond, Jr. July 4, 1939 FOREIGN PATENTS Number Country Date 836,555 France Oct, 17, 1938 352,035 Great Britain June 22, 1931 367,283 Great Britain Feb. 18, 1932 

